1. Field of the Invention
The present invention belongs to the field of the production of industrial vehicles, such as for example commercial vehicles and/or trucks. More precisely the invention refers to a device for water circulation in a cooling circuit of an internal combustion engine, preferably, but not exclusively, of the diesel type. The present invention further relates to a cooling circuit of an internal combustion engine comprising such device and to a commercial and/or industrial vehicle comprising said cooling circuit.
2. Prior Art
As it is known, any vehicle motorized by an internal combustion engine (e.g. diesel engine) must necessarily comprise a cooling circuit of the engine itself, in order to ensure its correct functioning. A cooling circuit of an internal combustion engine, usually comprises a circulation pump and a cooling line which develops downstream of the circulation pump passing through the cylinder block and the cylinder head of the internal combustion engine in order to cool them.
After the heat exchange with said engine elements, the water circulating in the cooling line flows into a radiator where it is cooled by a water/air heat exchange. The cooled air leaving the radiator is thus brought back to the inlet of the circulation pump in order to pass through the circuit again. Usually the cooling circuit comprises also a bypass line regulated by a the thermal expansion valve. More precisely, such thermal expansion valve has the function of diverting the water directed to the radiator into the bypass line when the temperature of the water is below a predetermined characteristic value, usually when the engine is in its start phase. When the water temperature exceeds such predetermined value, then the thermal expansion valve chokes/splits the water flow from the cooling line in a first fraction circulating in the bypass line and in a second fraction directed to the radiator. When the water temperature exceeds a second predetermined value, then the thermal expansion valve directs the whole water flow rate towards the radiator, blocking the passage in the bypass line.
In the most recent solutions, the water flow rate leaving the circulation pump (in the following indicated also by delivery flow rate) is regulated as a function of the operating conditions of the internal combustion engine, namely as a function of the load and of the speed of the engine itself. In particular, in partial load conditions, the delivery flow rate is reduced in order to limit the cooling of the engine and to avoid an overcooling of the cylinders, namely an overcooling of the oil. Such negative condition, indeed, would result in an increase of its viscosity and thus in an increase of the frictions of the engine. At present, the delivery flow rate regulation is performed according to two different solutions, which, however, are not advantageous in terms of costs, efficiency and reliability.
A first known solution provides the use of a control in order to vary, without depending on the engine, the speed of rotation of the pump. Such control is usually formed by an electric motor with adjustable speed which drives directly the impeller shaft of the pump. The reduction of the delivery flow rate is varied by varying the speed of the electric motor, which results in a variation of the speed of rotation of the impeller. The electric motor is controlled as a function of the water temperature and thus of the operating condition of the internal combustion engine. The variation of the speed of the impeller results in a variation of the pump head, and thus of the delivery flow rate.
Even though this solution is relatively effective in terms of delivery flow rate regulation, it has evident disadvantages in terms of efficiency. In particular, converting the energy that is necessary for the functioning of the electric motor is a very critical factor in terms of efficiency. Moreover, it has to be noted that in case of failure of the electric motor or of the circuit that controls the motor itself, the circulation pump will not work, and thus water will not circulate in the cooling line. In these conditions the risk of burning out the engine is high, since the heat is no longer dissipated. It is thus evident that activating the hydraulic pump without depending on the driving shaft is unacceptable in terms of reliability, above all for heavy industrial vehicles whose life usually exceeds one million kilometers.
An alternative known solution provides the use of an electromagnetic coupling between the pulley driven by the driving shaft by means of a mechanical transmission and the rotating shaft of the impeller of the hydraulic pump. The electromagnetic couplings allows, if necessary, a slipping between pulley and impeller, which implies a variation in the speed of the impeller itself, namely a variation of the delivery flow rate.
Compared to the previous solution, this second solution makes the engine more reliable, since in case of a failure of the electromagnetic coupling, the hydraulic pump keeps working, allowing the circulation of the cooling water. In terms of costs, however, the electromagnetic coupling is extremely expensive, and it has a very low efficiency, from an operating point of view, usually around 60%. This aspect is partially prejudicial to the reduction of absorbed power, above all at low speed. Consequently a relevant part of the power saving at the pump shaft is negatively compensated by the low efficiency of the transmission of the coupling. Even though the energy balance is positive, overall, this second solution is still unsatisfactory.
From these considerations, the need for an alternative technical solution, allowing to overcome the aforementioned limits and the drawbacks of the prior art, emerges.
Consequently the main task of the object of the present invention is to provide a device for water circulation in a cooling circuit of an internal combustion engine, which allows to overcome the drawbacks mentioned above.
In the scope of this task, a first aim of the present invention is to provide a device for water circulation which does not affect negatively the safety of the internal combustion engine in case of failure.
Another aim of the present invention is to provide a device for water circulation which is not based on the use of an electromagnetic coupling or of an electric motor.
Not least, the purpose of the present invention is to provide a device for water circulation which is reliable and easy to manufacture with competitive costs.